1. Field of the Invention
This invention is directed to an alignment mark used to align a mask to form a feature at a desired position on a substrate. The invention is also directed to a method for making the mark.
2. Description of the Related Art
In the formation of a magneto-resistive (MR) thin-film head device, the head device is integrated into a substrate so that it extends across a dice line. Upon dicing the side edge of the substrate, the head device is exposed in the substrate""s side edge. The substrate""s side edge is polished and subjected to selective removal of portions of the substrate and device through ion milling or reactive ion etching, for example, to form a relatively narrow write gap bridge. With its narrow width, the write gap bridge can be used to write correspondingly narrow data tracks on a magnetic storage device such as a hard disk drive. The narrow width of the data tracks allows the tracks to be more closely spaced to increase data density of a magnetic storage device with which the head device is used.
The selective removal of portions of the substrate and head device to form the write gap bridge must be performed with high accuracy so that the write gap is properly positioned with respect to the portion of the MR layer used to read data. To perform the selective removal of material in the proper locations, a resist layer is formed and patterned to selectively expose the appropriate portions of the substrate and head device. The current practice to align the mask used to form the resist layer for ion milling, is to use a specific component of the head device as a positional reference for alignment. However, the ideal reference component for alignment in a MR thin film head is the MR contact layer, which is extremely thin in width, usually from 0.1 to 0.2 microns. Accordingly, the alignment system has great difficulty detecting the head device""s reference component, if it is able to do so at all. Furthermore, by aligning to a component of the head device, the alignment system must be moved relative to the substrate before transfer of the mask pattern to the resist layer by exposure, thus introducing inaccuracy in the alignment of the mask used to form the feature. It would be desirable to overcome these disadvantages of previous devices and techniques for aligning features on the side surface of a substrate.
This invention overcomes the above-noted disadvantages. An apparatus in accordance with this invention includes an alignment mark that is formed in a substrate. The mark extends across a dice line so that, upon dicing the substrate, the mark is exposed in the substrate""s side edge. The mark is formed at a predetermined distance from a position at which a feature is desired to be formed on the substrate""s side edge using a mask. Accordingly, the mark is a positional reference that can be used for highly accurate placement of the feature with the mask. Preferably, the mark is formed of metal or other material with an enhanced size and appearance that are readily detectable by an alignment system with which the mark is to be used.
In a preferred configuration, the mark is formed with the same mask as that used to form a specific component of an integrated device in relation to which it is desired to form the feature. For example, the component can be the contact layers for the read gap of a thin-film head. The invented alignment mark is positioned at a predetermined distance from the component as determined by the mask. Like the mark, the integrated device is formed in the substrate and exposed in the substrate""s side edge upon dicing and polishing the substrate. Preferably, the mark is formed together with the component at a relatively early step in the manufacture of the integrated device so that the mark""s position is relatively unaffected by successive misalignments that generally occur over later steps in the integrated device""s formation.
The invented alignment mark can be used as a positional reference for a mask to form a variety of different kinds of features. For example, the aligned mask can be used to pattern a resist layer to expose two window portions on opposite sides of a write gap bridge for a thin-film head device. Portions of the substrate and integrated device that are exposed by the windows, are removed by ion milling or reactive ion etching, for example. The selective removal of the substrate forms features that in this case are recessed areas positioned on opposite sides of a central write gap bridge of the thin-film head device. The write gap bridge is defined by the recessed areas so that it corresponds closely with the device""s read gap composed of a MR layer situated between two contact layers. Because the alignment mark is formed together with the contact layer device components that define the read gap, the positioning of the write gap bridge can be controlled with the mark to closely align the write gap bridge with the read gap. By narrowing the width of the write gap bridge by the selective removal of material, and by properly aligning the read and write gaps relative to one another, the thin-film head device can read or write relatively thin, closely spaced data tracks on a magnetic storage medium such as a hard disk drive. The narrower width and closer spacing of the data tracks can be used to greatly increase the data density stored on the magnetic medium relative to conventional devices or techniques.
In addition to forming the recessed area features for the head device, the alignment mark can also be used to align a mask to form other types of features in relation to a head device or other types of integrated devices. For example, the alignment mark can be used to form an electrical connection to an integrated device such as transistor, diode, resistor, capacitor or other device exposed on the substrate""s side edge.
A method of this invention includes a step of forming a mark and an integrated device component in a substrate with a first mask, and a step of forming a side edge of the substrate exposing the mark and the component. The invented method also includes a step of aligning a second mask defining a feature with the mark, and a step of forming the feature relative to the component with the second mask. To make the mark more visible to a mask alignment system used to form the feature, in the step of forming the mark, the mark can be enhanced in size. The mark enhancement can be accomplished in the invented method in different ways. For example, the step of forming the mark can be performed with a first resist layer that defines the mark and component, that is removed in locations proximate to the mark to eliminate resist wall residue produced in forming the integrated device. A second resist layer is formed to cover the integrated device and expose the mark, and material is selectively deposited on the mark to increase its size. For example, such mark deposition can be performed by plating or chemical vapor deposition, for example, both of which are well-known techniques. Alternatively, the first resist layer used to form the mark and component can be left intact. To clean the side walls of the first resist layer that define the contact layer components and the alignment marks, the side walls can be subjected to ion bombardment or a reactive ion beam. A second resist layer is formed that covers the integrated device, but exposes the mark. The material is selectively deposited on the mark to enhance its size, for example, by plating, chemical vapor deposition or sputtering. The remaining steps in the process for forming the integrated device are completed. The resulting mark is readily detectable by an alignment system to align a mask to form a feature at a desired position on the substrate""s side edge.
The invented method can be used to accurately position a variety of different types of features on the substrate""s side edge. For example, the integrated device can be a MR head, and the feature can be recessed areas defined by a resist layer on opposite sides of the MR head device""s write gap. The invented method further includes a step of selectively removing portions of the substrate and head device exposed in the windows defined in the resist layer, to produce the feature recessed areas. The relatively narrow write gap bridge and its proper alignment to the read gap allows for correspondingly narrow data tracks to be written on a disk drive, for example, so that such tracks can be made relatively thin and more closely spaced, thus increasing the data density of the disk drive. The invented method can be used to form other types of features on the substrate""s side edge. For example, the feature can be a conductive line for making an electrical connection to the integrated device. The conductive line can be formed by patterning a resist layer with a feature mask that is aligned with the mark.
Advantageously, the mark of the invented apparatus and method allows for highly accurate positioning of a feature that is desired to be formed on a substrate""s side edge. This aspect of the invention is highly useful for a broad variety of applications, including the alignment of a mask for formation of recessed areas to reduce the width of a thin-film head""s write gap or to form a conductive line for coupling to an integrated device on the substrate""s side surface. Because the mark can be formed with a relatively large size in the invented apparatus and method, the mark can be readily detected and used as a positional reference by an alignment system for alignment of a mask used to form a feature on the substrate""s side edge. In addition, because the mark can be accurately positioned with respect to a particular component of an integrated device by formation with the same mask, the mark is a highly accurate positional reference for a feature mask used to form a predetermined feature at a desired position with respect to the component.
These together with other features and advantages, which will become subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being made to the accompanying drawings, forming a part hereof, wherein like numerals refer to like parts throughout the several views.